1. Technical Field
The present disclosure relates to a method for testing a microelectromechanical device and to a microelectromechanical device.
2. Description of the Related Art
As is known, several types of microelectromechanical sensors, dedicated to numerous applications, have recently been developed. Just to cite a few examples, amongst the microelectromechanical sensors that are increasingly frequently used there may be recalled linear and rotational accelerometers, gyroscopes, pressure sensors, acoustic sensors and transducers (microphones), and so forth. Generally, a microelectromechanical sensor comprises a first semiconductor chip, in which a microstructure with movable parts and fixed parts is made, and a second semiconductor chip, in which control, driving, and read circuits are integrated. The first and second semiconductor chips are bonded and electrically coupled to one another and are incorporated in a single package.
The microstructure defines the sensitive element of the device, and the circuitry is coupled thereto for converting the state and/or the movements of movable parts of the microstructure into signals indicating a physical quantity detected.
As with all electronic devices, microelectromechanical sensors can be tested by test devices that enable verification of their proper operation. As regards control, driving and read circuits, execution of tests both in the factory and in use does not entail particular difficulties, and dedicated integrated components or external components, coupled through the input/output terminals of the microelectromechanical sensors can be used for this purpose.
Things are instead different for the verification of the microstructure. Also this, in fact, is subject to malfunctioning that may derive from defects of manufacture or else from use, ageing, or any damage suffered. However, verifications of functionality of the microstructure are far from simple, since testing involves transmitting mechanical stresses (accelerations or force pulses) such as to cause a detectable response at output by the microstructure itself. In practice, a microelectromechanical sensor is subjected to a known stress, and its output is monitored.
If the signals supplied in response are compatible with the stress undergone, the test is passed; otherwise, the microelectromechanical sensor is rejected.
It is, however, evident that, owing to excessive cost in terms of time, tests of this sort can be conducted only on a restricted sample of sensors, whereas it would be desirable to have available methods and sensors suited for conducting verifications of proper operation on a vast scale and, in particular, after the devices have left the factory.